1. Field of the Invention
The present invention relates to a signal transmitting method and apparatus in a mobile communication system using multiple antennas.
2. Description of the Background Art
In most coded modulation systems used in a wireless environment, gray mapping is performed on data (symbols) of 8 PSK (Phase Shift Keying) or 16 QAM (Quadrature Amplitude Modulation). For example, FIG. 1 illustrates a constellation using gray mapping for 16 QAM.
As shown in FIG. 1, when gray mapping is used, four bits are required to form one symbol of 16 QAM. In a HSDPA (High Speed Downlink Packet Access) system using a HARQ (Hybrid Automatic Repeat Request) function the data is transmitted via an antenna and is received by a receiver. If a retransmission is required, the order of bits of data that has been first transmitted is changed and then the data is retransmitted. Such an operation is called a constellation rearrangement.
The related art signal transmitting method is applied to a communication system having one transmission/receive antenna. However, currently there are Multiple Input Multiple Output (MIMO) communication systems having multiple transmitting antennas and multiple receiving antennas. In these type of systems, the independency of the symbols transmitted from each transmit antenna must be maintained to properly detect the transmitted symbols. However, the independency of the channels is not always maintained resulting in the symbols being not detected properly.